1. Field of the Invention
The invention relates to an encoder with a housing, which can be assembled, for flanging at the front end to a motor 1, which has a motor shaft 2 protruding into the housing at at least one flange plane, the housing consisting of a base plate 4 with an inner part 4a and an upper part 11 of the housing, which can be fitted into one another for the assembly. On the inner part 4a of the housing, bayonet segments 12a are disposed, which engage corresponding recesses 12b of the upper part of the housing. Furthermore, at the bayonet segment 12a, guiding surfaces 5a are constructed, which form a sliding guide with corresponding counter surfaces 5b at the upper part of the housing and which, when inserted, bring about a separation of the upper part 11 from the base plate 4 by rotation in the peripheral direction. In a roof surface of the upper part of the housing, a contact surface 16 for adjusting a timing disk 10 on the motor shaft 2 is formed concentrically with the latter.
2. Description of the Related Art
An encoder of the type mentioned above is known from the DE 196 41 926 A1 (RUHLATEC Industrieprodukte GmbH). The timing disk holder, described there, is held by a retaining ring 14 in the pre-assembled state in the housing unit and, by these means, prevented from inadvertently falling out of the housing. The retaining ring 14 has adequate clearance for centering the timing disk on the motor shaft while the upper and lower parts of the housing are being assembled.
In the case of shafts of larger diameter (more than 3 mm), the assembly becomes very difficult because of the pressing-on forces, which constantly become larger. The surface quality of the motor shaft and the timing disk hub must be very high, so that jamming cannot occur even when the fit tolerances are very tight. A further problem consists therein that, after the assembly is completed, there must be a so-called xe2x80x9cunlockingxe2x80x9d of the timing disk. This means that the housing is distanced from the timing disk only by rotating the bayonet surfaces; the timing disk then runs freely on bearings on the motor shaft. Here also, there can be problems with the retaining ring.
It is therefore an object of the present invention to make it possible, in the case of an encoder of the type named above, to secure the timing disk before the assembly and the unlocking after the assembly in such a manner that, on the one hand, a central position in relation to the motor shaft is maintained even under more difficult installation and transporting conditions and, on the other, a reliable unlocking can take place after the upper part of the housing is fitted together with the base plate, which is connected with the motor shaft.
Pursuant to the invention, this objective is accomplished by the distinguishing features given in the claims. It has turned out that a reliable centering and unlocking becomes possible when a fork with prong openings of different width is used.